The heat could be felt for more than a block away as a four-alarm fire destroyed a construction site in Salt Lake City on Sunday night.

The SLC Fire Department responded to the scene near 550 East 500 South before 6 p.m. Within 90 minutes, the fire was under control.

Jasen Asay, SLCFD public relations officer, said fire department investigators are currently inspecting the incident. They are expected to enter the building this morning, Feb. 11.

Before firefighters can reenter the premises, the top two floors of the remaining structure will be collapsed with a wrecking ball to ensure the walls do not cave in on investigators. The building, under construction by U.S. Development, was an anticipated multi-residential facility with 61 apartment spaces and four floors.

SLCFD responded to the scene with approximately 60 firefighters, 10 engines and four trucks because of the magnitude of the flames. Crews watched the fire over night to ensure no hot spots reignited. Asay said remaining hot spots were extinguished Monday morning.

“We haven’t been able to go inside the building yet, just because of the hot spots earlier and because it could be structurally unsafe,” Asay said. “But we really need to get inside and do some digging in the remains of the building before we can try to start to figure it out.”

The cause of the fire is currently unknown, and the SLCFD has no speculation or leads. According to a SLCFD press release, the fire caused an estimated loss of more than $1.5 million. A construction crane was melted by the heat of the flames and has since been disassembled at the scene.

Asay said U.S. Development reported that no workers were in the building at the time and no active power or heat sources were located inside.

“We won’t be able to rule anything out until we actually go in and start to investigate inside the building,” Asay said.

A main concern for the SLCFD in the fire was the potential for sparks to ignite surrounding buildings. The Smith’s Market Place north of the incident was evacuated, as well as an adjacent building to the construction site. Firefighters doused the roof of Smith’s and the walls of the nearby buildings in water to prevent the embers from spreading, Asay said.

He said this concern was heightened because the construction site had a large quantity of exposed wood.

“It went from a first-alarm to a second-alarm fire really quickly. And then once our incident commander was on site, we realized what was going on,” Asay said. “A lot of times with four-alarm fires, it does escalate that quickly.”

Upon arriving at the scene, SLCFD officers hoped to extinguish the fire offensively by starting from inside the building. Asay said because of the flames and the unstable structure of the building that initial approach would have been ineffective.

A man was also detained and charged for impersonating an officer at the scene of the fire. Josh Murray, a 27-year-old man, bypassed restricted personnel lines under a false persona as a SLCFD crew member. Murray is not a suspect in the fire, but Asay said he put himself and others in danger.

The responding firefighters were completing the end of their regular two-day shift when they received the call. SLCFD firefighters work for 48 hour shifts and then have 96 hours off-duty. Those who responded to the fire at 6 p.m. Sunday night were set to be relieved at 8:30 a.m. Monday morning. Asay said despite being tired, the firefighters are “doing good.”

“I imagine that they’re getting some rest,” Asay said. “Hopefully they will be able to catch up on that rest and for the next [couple] days before they come back to work.”

Asay was unsure how long construction at the site has been underway, and U.S. Development did not immediately return calls for comment.